This volume considers the transport of molecules, large and small, across the membranes of prokaryotic and eukaryotic microbial cells. A diverse range of related phenomena are covered, but the unifying themes are the signal peptides that target proteins to particular destinations, and the role of chaperonins. Topics covered include: secretion of proteins out of the bacterial cell by Type I, II and III mechanisms, including the newly recognised bacterial signal recognition pathway in Type II; passage across internal membranes of eukaryotic proteins, whether destined for secretion or en route to internal organelles such as chloroplasts and peroxisomes; how bacteria obtain the energy required for solute uptake, the role of phosphorylation, and evolutionary relationships of some of the proteins involved; and efflux pumps for toxic substances in bacterial, animal and plant cells.